_toupper man page


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

_toupper — transliterate lowercase characters to uppercase


#include <ctype.h>

int _toupper(int c);


The _toupper() macro shall be equivalent to toupper() except that the application shall ensure that the argument c is a lowercase letter.

Return Value

Upon successful completion, _toupper() shall return the uppercase letter corresponding to the argument passed.


No errors are defined.

The following sections are informative.

Application Usage

Applications should use the toupper() function instead of the obsolescent _toupper() function.

Future Directions

The _toupper() function may be removed in a future version.

See Also

islower(), toupper()

The Base Definitions volume of POSIX.1‐2008, Chapter 7, Locale, <ctype.h>


2013 IEEE/The Open Group POSIX Programmer's Manual